1. Field of the Invention
The present invention relates to a novel human defensin peptide. More specifically, isolated nucleic acid molecules are provided encoding a human antimicrobial peptide. Antimicrobial polypeptides are also provided, as are vectors, host cells and recombinant methods for producing the same. Also provided are diagnostic methods for detecting disorders related to the immune system and therapeutic methods for treating such disorders.
2. Related Art
One of the key roles of the respiratory epithelium in mammals is to form a barrier to potentially harmful environmental threats. A number of defense mechanisms have been identified that protect the respiratory tract from airborne agents that are thought to be responsible for airway disease, such as infectious agents, gases and particulates. (Newhouse et al., "Respiratory Tract Defense Mechanism" Textbook of Pulmonary Disease, Little Brown and Co. (1989)). The recent identification and characterization of antimicrobial peptides from a variety of species has unveiled a new member of the animal host defense system and are believed to participate in the defense against potential microbial pathogens. These newly identified antimicrobial peptides families include cecropins, magainins, and defensins. Cecropins were the first well-characterized family of structurally related antimicrobial polypeptides and are found in a wide distribution of insects. (Bowman et al., Ann. Rev. of Microbiol. 41:103 (1987)). In vertebrates, the magainin family of antimicrobial peptides have been isolated from the glands of the skin and gastrointestinal tract of Xenopus laevis, and are thought to form the basis for defense system of the amphibian mucosal surfaces against infection. (Soravia et al., FEBS Lett. 228:337 (1988); Zasloffet al., Proc. Natl. Acad. Sci. 84:5449 (1987)). Defensins are antimicrobial peptides found in phagocytic cells isolated from several mammalian species including man and may be characterized by eight invariant residues within the sequence. (Gabay et al., Curr. Opin. Immunol. 1: 36 (1988); Gabay et al., Proc. Natl. Acad. Sci. 86:5610 (1989); Ganz et al., Infect. Immun. 55:568 (1987); Ganz et al., J. Immunol. 143:1358 (1989); Ganz et al., J. Clin. Invest. 76:1427 (1985)).
The mechanism of antimicrobial activity of peptides such as the defensins is via a selective membrane disruption leading to a characteristic broad spectrum of antibiotic activity. (Bowman, Ann. Rev. of Immunol. 13:61 (1995)). The antimicrobial spectrum of defensins includes gram positive and gram negative bacteria, mycobacteria, T. pallidum, many fungi, some enveloped-viruses. (Bowman, Ann. Rev. of Immunol. 13:61 (1995)). Defensins exert nonspecific cytotoxic activity against a wide range of normal and malignant targets, including cells resistant to TNF-.alpha. and NK-cytolytic factor. They appear to kill mammalian target cells and microorganisms by common mechanism which involves initial electrostatic interactions with negatively charged target cell surface molecules, followed by insertion into the cell membranes which they permneabilize, forming voltage regulated channels. (Lehrer et al., Ann. Rev. of Immunol. 11:105 (1993)).
In addition to their antimicrobial and cytotoxic properties, some defensins act as opsonins, while others inhibit protein kinase C, bind specifically to the ACTH receptor and block steroidogenesis or act as selective chemoattractins for monocytes. Defensins are newly delineated family of effector molecules whose contribution to host cell defense, inflammation, and cytotoxicity may be considerable for humans. (Lehrer et al., Ann. Rev. of Immunol. 11:105 (1993)).
Defensins are basic peptides 30-34 amino acids with three disulfide bonds. The known characterized defensins for both myeloid and nonmyeloid tissues all have highly conserved amino acid residues within the family, including 6 invariant cysteins. Recent studies have found that similar antimicrobial peptides are also made by certain epithelial cells suggesting an additional role in the defense of mucosal surfaces. (Diamond et al., Proc. Natl. Acad. Sci. 90:5496 (1993); Diamond et al., Proc. Natl. Acad. Sci. 88:3952 (1991); Eisenhauer et al., Infect. Immun. 60:3556 (1992); Jones et al., J. Biol. Chem. 267:23216 (1992); Schonwetter et al., Science 267:1645 (1995); Selsted et al., J. Cell. Biol. 118:929 (1992)).
Tracheal antimicrobial peptide (TAP) is a 38 amino acid peptide isolated from the bovine respiratory mucosa and was the first member of what is now recognized as arelatively large family of antimicrobial peptides, .beta.-defensin, all of which have broad spectrum antimicrobial activity in vitro. (Diamond et al., Proc. Natl. Acad. Sci. 88:3952 (1991)). Recently a second .beta.-defensins of epithelial origin, lingual antimicrobial peptide (LAP) was isolated from bovine tongue. (Schonwetter et al., Science 267:1645 (1995); Selsted et al., J. Cell. Biol. 118:929 (1992)).
Thus, there is a need for polypeptides that function as antimicrobial or immune regulators, since disturbances of such regulation may be involved in disorders relating to infectious diseases, inflamrnation and immune disorders.